RESULTS OF SOFT-PORK INVESTIGATIONS, II 7 
as the total amount of the predominating unsaturated acids (oleic 
and linolic) may vary according to the rations employed. The same 
situation may prevail in the case of the saturated acids (stearic and 
palmitic) although recent data (-5) show approximately twice as 
much palmitic acid as stearic acid. The results of fatty-acid analyses 
(2) have shown that the body fats from hogs fed different feeds vary 
widely in their fatty-acid composition. Lards from hogs fed on soy 
beans have been found to contain nearly equal quantities of oleic and 
linolic acids, while lards from hogs fed brewers' rice as the basal feed 
contained a relatively high amount of oleic acid and very little linolic 
acid. Lards of apparently equal firmness have been found to have 
differing proportions of fatty acids. Although little is known of the 
nature of the glycerides, it is evident that those formed during the 
feeding of a softening ration followed by a hardening ration may be 
*• materially different from those formed during the simultaneous feed- 
ing of softening and hardening feeds. 
It has been stated (J) that comparison of the various fat constants 
during the present investigations has shown that the melting point 
was less reliable than the refractive index or iodine number as a 
measure of firmness. Of the two latter methods, the refractive index 
has been adopted as the routine test. Under the uniform conditions 
prevailing in the handling of the fat samples and in making the 
refractive-index readings this test has shown a slightly higher corre- 
lation with committee grades and has been more useful because of 
the rapidity of determination as compared to the iodine number. 
The readings on preliminary fat samples which are available for 
comparison at the time the carcasses are graded have been particu- 
larly valuable. The refraction of unsaturated acids is known to be 
higher than that of saturated acids. This probably largely explains 
the parallelism of iodine and refraction values as associated with 
lard and renders the determination of both values unnecessary in the 
majority of cases. 
Inability to explain certain cases of marked irregularities between 
grades and refractive indexes was noted early in the work. It was 
also apparent that there were conditions under which a single scale 
of grade limits was not entirely applicable. The following statement 
was accordingly made in Department Bulletin 1407 (4, p> 11) : 
The refractive index does not always give an exact measure of the firmness of 
the hog carcass. In some cases the discrepancy in the refractive index as indi- 
cated by the committee grading is due to the nature of the adipose tissue, 
particularly its thickness and fat content ; in other cases it appears to be due to 
the specific effect on the fat of a certain kind of feeding. However, the refrac- 
tive index not only gives a check on the gradings but it furnishes a satisfactory 
means of comparing and showing slight changes in the degree of firmness which 
are not shown well by the gradings alone. 
Further study of the subject has accordingly been made from avail- 
able data on fat constants as well as on fatty-acid separations. Grade 
limits for refractive-index and iodine-number values have been deter- 
mined wherever possible to cover the lines of experimental feeding 
thus far reported. Particular attention has been given to the results 
on the back fat, since it has been found to be representative of the 
entire body fat. The difference between leaf fat and back fat varies 
somewhat with the ration used. Leaf fat is occasionally as soft as 
the back fat. The tabulation of refractive-index values according to 
71373°— 28 2 
